Took the heads off the 406 to check the pistons. Well, the heads are also being used on my next build...
Took a pic of all 8 cylinders.. I don't see any unusual wear.. There are carbon deposits on all 8 pistons but that doesn't seem to be out of the normal.. The bores seem fine with no unusual wear.. I don't see any indication of detonation etc.. but I'm not an expert.. Does anybody see anything unusual?

 

For whatever it's worth, I don't see any problems either. THe little bit I did see, when I blew up the pic just looked like dirt...


(at least on that end of the rods..

 

You had a spun bearing, Right? Anything else?

 

I haven't looked on the bottom end yet.. Might do that on the weekend.. The top end looks good..

All the symptoms point to bearing failure... (oil pressure jumping like crazy and a loud knocking noise from inside the engine)

 

Continued tearing down the 406. Pulled all main caps off (except the one with the oil pump attached)..

NONE of the bearings was spun....

I checked the oil and filter and didn't find excessive metal particles either.. However, I did find a few larger metal particles at the oil pump pickup..
Now I have a few questions:
Is there anything specific to consider when removing the bearing to which the oil pump attaches?
Do I have to remove the oil pump first?
What torque do I have to torque the main caps on a standard 4-bolt 400 block?

Now I want to check the rod bearings.
Is there anything specific to consider when checking those?
Are they the same way like main bearings?

If those turn out to be ok, I'm stumped... There was a noticeable knocking noise from inside the engine and the oil pressure was not steady which would point to a spun main bearing..
Any help or advice is appreciated!!

 

Sounds like a spun rod bearing to me. do some pushing around on your
rods to help find the bad one.

 

9 times out of 10, a knock is the rod bearing.

 

OK.. I continued the teardown...

Removed one rod cap after another...

Started with #8 and worked my way to #1..

8... good... 7... good.. 6... good... 5... good.. 4... good.. 3.... good.. 2..... good..

At this point, I started thinking that I'm tearing down a perfectly good engine... Well, the single last item that I was going to check was the problem.. Rod bearing #1 was badly spun.. It actually broke apart and both bearing ends were partly on top of each other..

Here are the pics... It's not a pretty sight...




Now I wonder what I'll have to do? I checked the cap and the crank (at that bearing) and it doesn't seem like the cap or crank have significant wear at rod bearing #1..
Will the crank have to come out and will it have to be completely machined OR can I just have the crank machined at the bearing that was shot and install oversized bearings there? All other bearings on the entire engine are fine...

 

at the very least pull the crank, get it miked and hopefully ONLY polished, the rods should be checked for size as well...you might check into coated bearings (mine come from Calico)...a little more money but they can take a bunch more abuse......redvetracr

 

the way the bearings look, I think you will have to turn the crank....pull your fingernail accross the crank's surface....you will feel the score marks, if any. If you do, then a polish may clean the crank, else the crank will have to be turned.

 

I'll check the crank tonight.. It didn't appear to be too bad when visually inspecting the crank, but I'll check tonight if there are any major score marks..

 

You might get away with just polishing the crank but then you might have to turn it .010 also. Check it and then have the machine shop take a look. Check out the rod also. You might be able to save it or you might have to replace just the 1 rod. Turn the crank and replace 1 rod at the worst is not a bad deal. Far cheaper than replacing the whole short block. Keep us posted.

 

Well, I'm having another engine built anyways.. I might rebuild the old 406 myself (except for the machine work) and get some heads with higher chamber cc (for lower compression) and put the engine into my yellow '68.. If I drop the compression to about 10.8 : 1, I'll be able to run pump gas in it and still make well over 500 HP

 

That'll work.

 

I can't imagine the crank not needing to be turned from that pic. It was a new crank....so hopefully a .010 cut is all that is needed.

Normally you turn all the rods at least so they are all the same. Now you *could* Bubba it and turn one rod journal and use undersized bearings on just those two...but that's not the right way. If the mains are still perfect, you could just turn all the rods and polish the mains (leaving them std) and you would be ready to go.

What bearings are in it? Are they H series Clevites or regular replacement ones? Look on back of a good one and get the part numbers

Just for fun....you will often find GM warranty motors like this these days. They will bore one cylinder .040...or turn rods .050 on one journal or whatever...it's all about what is cheapest. So if you ever get in a deal where the dealer wants to replace your motor and you're thinking "hey great...I'll get a new motor"...you would probably be better off making them fix your old one!!

Back to yours Oliver......the one that failed is the last rod to get oil. It's at the end of the line..furthest from the pump. Looks like maybe oil starvation. Pretty common deal when pulling wheelies and stuff. What pan do you have and how much oil do you run in it? Windage trays? Might look into an extra baffle to keep oil from climbing the back of the pan. What weight oil do you use? How warm is oil before you make a pass? I usually use some lighter oil at the track because I pull to line with motor pretty cool. Might look into the oil Accumulator from Moroso to give a little insurance. What clearances do you have in it? Maybe another .0005 would help rods? Using the coated bearings wouldn't hurt either....but double check clearances..they will be slightly tighter.

You will definitely need to tear it all apart and clean all the debris out of it. That bearing stuff will be everywhere.

Either need to resize that rod or buy a new one.

What oil fitler do you use? Might look into one of the 2qt truck style long ones to cut oil restriction. Moroso makes a good one...as well as the WIX or NAPA race style filters.


Good luck..the good news is it's a relatively easy fix.


JIM

 

Bearings are Clevite 77. My oil pan is a Moroso Drag Pan. It's a regular 7 qt Moroso oil pan... I'll post a pic of the inside...
I'm using the largest truck type oil filter and it's a K&N...
I ran Royal Purple 10W40.
As for the rod, I might get a new one but haven't decided yet.. The wear on the rod and cap didn't look all that bad.. Will post pics.. I think that I caught the spun bearing shortly after it happened...and the damage seems to be minimal.. Good that I didn't keep on running

Thanks for the information!!

 

As Jim suggested, re-size the rod first. Cost is chump change compared to the price of a new rod. The amount of metal taken to resize the rod is minimal without any affect on the rod's strength.

 

You want to run the "H" bearings Jim mentioned.

If anybody was a candidate for block oil restricted top end it would be you! keep that 10W-40 purple on the rods and mains. It also returns it to the pan faster. Most oil resticors come with .060 flow holes. Drill them out to .080 to increase the flow to the top end somewhat.

 

maybe it`s dry sump time??
...redvetracr

 

Thanks

Well, I'm using Eagle H-beam rods which aren't too expensive...